Development of a downsized and lightweight transducer having high flexibility utilizing a polymer material such as a dielectric elastomer has been progressed. As one example of the transducer, an actuator can be configured by interposing an elastomer dielectric film between a pair of electrodes (see Patent Documents 1 to 3, for example). In an actuator of this type, electrostatic attractive force between the electrodes increases with an increase of the voltage that is applied between the electrodes, so that the dielectric film that is sandwiched between the electrodes is compressed in the thickness direction and the thickness thereof decreases. As the film thickness decreases, the dielectric film correspondingly expands in the direction parallel to the electrode plane. As the voltage that is applied between the electrodes decreases, on the other hand, electrostatic attractive force between the electrodes decreases so that the compressive force acting on the dielectric film in the thickness direction decreases and the thickness thereof increases due to elastic restoring force thereof. As the film thickness increases, the dielectric film accordingly contracts in a direction parallel to the electrode plane. The electrode is fixed to both surfaces of the dielectric film in the thickness direction thereof. Therefore, it is required that the electrode be expandable/contractible in accordance with a deformation of the dielectric film so as not to hinder expansion and contraction of the dielectric film.
For example, a commercially available silver paste in which a silver powder is blended with a binder resin is poor in flexibility. Namely, the binder itself has a high elastic modulus and is highly filled with silver powder, so that the silver paste has a high elastic modulus and a low elongation at break. Therefore, when the silver paste is widely stretched, a crack occurs and the electric resistance extremely increases. When the silver paste is used for an electrode of an actuator, it cannot follow expansion and contraction of the dielectric film and it might inhibit a movement of the dielectric film.
On the other hand, for example, Patent Document 2 describes that a carbon nanofiber adheres to both surfaces of a dielectric film in the thickness direction thereof to form an electrode. Patent Document 3 describes that from a paste in which a conducting agent such as carbon black is blended with a binder such as an elastomer, an electrode is formed.